EUVD-2026-51486
GHSA-2w88-g477-cxmj
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Network-reachable but AC:H due to required reverse DNS control; no credentials needed; only limited client-configuration integrity impact, no confidentiality or availability effect.
Primary rating from Vendor (redhat).
CVSS VectorNVD
Lifecycle Timeline
2DescriptionNVD
A flaw was found in the keycloak-services component of Keycloak, which provides identity and access management services. The issue occurs when a realm administrator uses a wildcard domain (like *.example.com) to restrict which hosts can register or update clients. Due to improper validation, the system accepts any hostname that ends with the specified domain suffix, even if it is not a legitimate subdomain. An attacker who can control the reverse DNS of their connection can bypass these host-based restrictions, potentially allowing unauthorized client modifications.
AnalysisAI
Wildcard domain validation in Keycloak's keycloak-services component can be bypassed by an attacker who controls their connection's reverse DNS, enabling unauthorized client registration or modification against a Keycloak realm. The flaw stems from the system accepting any hostname that merely ends with the configured domain suffix (e.g., 'attackerexample.com' satisfying a '*.example.com' restriction) rather than enforcing true subdomain membership. Exploitation requires high attack complexity due to the reverse DNS control prerequisite, and no public exploit or CISA KEV listing has been identified at the time of analysis.
Technical ContextAI
The keycloak-services component implements host-based restrictions on client registration and update operations, allowing realm administrators to configure wildcard domain patterns (e.g., '*.example.com') to permit only trusted hosts. CWE-20 (Improper Input Validation) describes the root cause: the validation logic performs a suffix-match check rather than a proper subdomain parse, failing to verify the presence of a subdomain delimiter before the domain component. A hostname such as 'attackerexample.com' satisfies a suffix check against 'example.com' but is not a legitimate subdomain of 'example.com'. Because Keycloak uses the connecting client's hostname - resolvable via reverse DNS - for this check, an attacker who controls their server's PTR record can craft a reverse DNS entry to satisfy the flawed validation. Affected products per CPE data include Red Hat Build of Keycloak, Red Hat Single Sign-On 7, Red Hat Data Grid 8, and Red Hat JBoss Enterprise Application Platform Expansion Pack.
RemediationAI
Patch availability per vendor advisory: a patch is available per Red Hat advisory (https://access.redhat.com/security/cve/CVE-2026-18206), but an exact patched version number is not confirmed in the available intelligence - consult the Red Hat advisory and Bugzilla entry (https://bugzilla.redhat.com/show_bug.cgi?id=2508292) for the specific fixed build. As an immediate compensating control, realm administrators should replace wildcard domain entries in client registration policies with explicit, fully qualified domain names (e.g., replace '*.example.com' with 'app.example.com', 'api.example.com') - this eliminates the suffix-match ambiguity entirely, though it requires enumerating all legitimate subdomains and increases administrative overhead when new subdomains are added. Alternatively, restrict client registration and update operations to authenticated realm administrators only, removing reliance on host-based restrictions as an access control mechanism.
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External POC / Exploit Code
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